Michael A. Grasso David S. Ebert Timothy W. Finin The Integrality of Speech in Multimodal Interfaces. 303-325 1998 5 ACM Trans. Comput.-Hum. Interact. 4 http://doi.acm.org/10.1145/300520.300521 db/journals/tochi/tochi5.html#GrassoEF98